1. Field of the Invention
The present invention relates to a composition comprising at least one organosilicon compound A comprising at least two hydrolyzable and condensable groups, which may be identical or different, or at least two silanol functions ≡SiOH, which are crosslinkable, curable or vulcanizable at room temperature into elastomer by polycondensation and which do not contain any alkyltin-based catalysts that have toxicity problems.
2. Description of Related Art
The invention also relates to novel polycondensation catalysts in the chemistry of silicon compounds and in particular in the chemistry of silicones and to the uses thereof as catalysts for the polycondensation reaction of silicon compounds comprising at least two identical or different hydrolyzable and condensable groups, or at least two silanol functions ≡SiOH.
Formulations of silicone compositions that crosslink via polycondensation generally involve a silicone oil, generally a polydimethylsiloxane, with hydroxyl end groups, optionally prefunctionalized with a silane so as to have hydrolyzable and condensable ends, a crosslinking agent, a polycondensation catalyst, conventionally a tin salt or an alkyl titanate, usually with a reinforcing filler and other optional additives such as bulking fillers, adhesion promoters, colorants, biocidal agents, etc.
These silicone compositions which “cure” by polymerization and/or crosslinking at room temperature are well known to those skilled in the art and are classified into two distinct groups:                one-pack compositions (RTV-1), which are in the form of only one part (or component) whose packaging is airtight, and        two-pack compositions (RTV-2), which are in the form of two distinct parts (hence the name “two-pack”) and whose packaging containing the catalyst is airtight.        
The purpose of the airtight packagings is to avoid the silicone compositions containing the catalyst from coming into contact with atmospheric moisture during storage before use.
During curing (by polymerization and/or crosslinking) of these silicone compositions, the water is provided by the atmospheric moisture in the case of the RTV-1 products. In the case of the RTV-2 products, dimethyltin dicarboxylates are commonly used as catalysts, but they require the addition of an amount of water to one of the parts in order to activate the catalyst and to allow the polycondensation reaction when the contents of the two parts are mixed in ambient air so as to form the elastomer network, which is reflected by curing of the composition.
For example, the one-pack silicone compositions (RTV-1) used as mastics or adhesives crosslink without heating according to a mechanism involving a certain number of reactions that may be successive or simultaneous:
a) functionalization which results from the placing of a silicone oil bearing silanol functions in contact with a crosslinking agent, occasionally known as a “scavenger”, such as a silane compound of SiX4 type (for example a silicate) or a compound bearing the following function —SiX3 with X usually being an alkoxy, acyloxy, amino, amido, enoxy, aminoxy, ketiminoxy or oxime function, which are well known for being reactive with silanol functions. The resulting product is usually known as a “functionalized oil”. This reaction may be desired directly during the preparation of the composition or optionally as a pre-step before the addition of the other components of the composition. In this pre-step, it is common practice to use a functionalization catalyst, for instance lithium hydroxide or potassium hydroxide so as to give the one-pack composition good stability on storage. To do this, a person skilled in the art may choose specific functionalization catalysts and will adjust the amount of the reagents so as to have a molar excess of crosslinking agent relative to the silanol functions to be functionalized, and
b) crosslinking via a hydrolysis of the functionalized oil generally performed by means of water vapor which diffuses into the material from the surface exposed to the atmosphere, and a condensation between the silanol groups formed and other residual reactive functions.
Generally, the polycondensation reaction kinetics are slow. These reactions are thus catalyzed with a suitable catalyst. As catalysts that are used, use is most often made of catalysts based on tin, titanium, an amine or compositions of these catalysts. Catalysts based on tin (cf. in particular FR-A-2 557 582) and on titanium (cf. in particular FR-A-2 786 497) are catalysts that are effective.
As regards the RTV-2 two-pack compositions, they are sold and stored in the form of two components (or parts), a first component (or part) comprising the polymers that are capable of polycondensing and the second component is airtight and contains the catalyst and usually the crosslinking agent. The two components (or parts) are mixed during use and the mixture crosslinks in the form of a relatively hard elastomer when the composition comprises reinforcing fillers. These two-pack compositions are well known and are described, in particular, in the book by Walter Noll “Chemistry and Technology of Silicones” 1968, 2nd Edition, on pages 395 to 398. These compositions essentially comprise 4 different ingredients:                a reactive polymer such as an α,ω-bis(hydroxydimethylsilyl)polydimethylsiloxane,        a crosslinking agent,        a condensation catalyst, and        optionally water, which is usually present when a dialkyltin dicarboxylate is used as catalyst (activation of this catalyst by the presence of water).        
Usually, the condensation catalyst is based on an organic tin compound. Indeed, many tin-based catalysts have already been proposed as a catalyst for crosslinking these RTV-2 products. The most widely used compounds are alkyltin carboxylates such as tributyltin monooleate or dialkyltin dicarboxylates such as dibutyltin dilaurate, dibutyltin diacetate or dimethyltin dilaurate (see the book by Noll “Chemistry and Technology of silicones” page 337, Academic Press, 1968—2nd Edition or patents EP 147 323 or EP 235 049).
However, the alkyltin-based catalysts, although very effective, usually colorless, liquid and soluble in silicone oils, have the drawback of being toxic (CMR2 toxic for reproduction).
Titanium-based catalysts, which are also extensively used in RTV-1 products, have, however, a major drawback: they have slower kinetics than tin-based catalysts. Furthermore, these catalysts cannot be used in RTV-2 compositions due to gelling problems.
Other catalysts are sometimes mentioned, such as catalysts based on zinc, zirconium or aluminum, but they have only experienced minor industrial development due to their mediocre effectiveness.
For sustainable development, it therefore appears necessary to develop nontoxic catalysts for the polycondensation reaction of organopolysiloxanes.
Another important aspect for an organopolysiloxane polycondensation reaction catalyst is the pot life, that is to say the time during which the composition can be used after mixing without curing. This time must be long enough to allow it to be used, but short enough to obtain a molded article that can be handled at the latest a few minutes or a few hours after it has been manufactured. The catalyst must thus make it possible to obtain a good compromise between the pot life of the catalyzed mixture and the time at the end of which the molded article can be handled (these times depend on the targeted application such as, for example, the molding or manufacture of seals). In addition, the catalyst must confer, on the catalyzed mixture, a spreading time which does not vary as a function of the storage time.